The conversion of methylenic carbons to ketones, e.g., the conversion of cyclohexane to cyclohexanone, is important in the manufacture of useful synthetic materials. Indeed, cyclohexanone is the principal starting material in the synthesis of adipic acid which in turn is used to make nylon and dacron. In addition, the ability to dioxygenate organic substrates would afford numerous alternatives in the total synthesis of pharmaceuticals and biomolecules, e.g., antibiotics, steroids, hormones and the like. Thus, the utility and desirability of efficient and inexpensive methods for the conversion of methylenic carbons to ketones and for the dioxygenation of organic substrates are manifest.
Several reports (1-5) have described the selective transformation of methylenic groups (&gt;CH.sub.2) to ketones via four heterogeneous iron-dioxygen systems; (a) iron powder/sodium sulfide/O.sub.2, (b) Fe.sub.3 O(OAc).sub.6.3.5 pyridine(py)/zinc dust/O.sub.2, (c) (py).sub.4 FeCl.sub.2 /KO.sub.2 (s), and (d) (py).sub.4 FeCl.sub.2 /(O.sub.2 +e.sup.- .fwdarw.O.sub.2.sup.-.) in 4:1 pyridine/acetic acid. These systems are postulated to contain .sigma.-bonded iron-carbon intermediates (6) with superoxide ion (O.sub.2.sup.-.) as the active form of reduced oxygen, which oxidizes the iron catalyst within the catalytic cycle. Pyridine is believed to be essential to the system as a trap for hydroxyl radical, thereby preventing Fenton chemistry. Acetic acid serves as a proton source to transform superoxide ion to hydroperoxyl radical (HOO.sup..). However, these heterogeneous iron-dioxygen systems proved to be inefficient and resulted in the indirect production of hydrogen peroxide from superoxide ion.
Other experiments with other iron complexes, or other solvent matrices, are reported to yield a spectrum of products that are characteristic of Fenton chemistry (.sup.. OH) (4). In addition, it has been reported (7) that [Fe(MeCN).sub.4 ](ClO.sub.4).sub.2 in anhydrous acetonitrile activates excess HOOH for the dioxygenation of diphenylisobenzofuran, rubrene, acetylenes, cis-stilbene, and methylstyrene. However, the system is essentially unreactive with saturated hydrocarbons, and the presence of basic ligands (H.sub.2 O or pyridine) causes the system to promote Fenton chemistry [Fe(II)+HOOH.fwdarw.Fe.sup.III OH+.sup.. OH] (8).